This invention relates to a novel water-dispersible resin having quarternary ammonium groups. It also relates to a pigment paste composition and a coating composition for use in cathodic electrodeposition coating systems.
Polybutadiene-based cathodic electrodepositing coating compositions are known. These compositions contain a cationic water-dispersible resin produced by reacting partially epoxydized homopolymers or copolymers of butadiene, a primary or secondary amine and optionally acrylic or methacrylic acid. See, Japanese Laid Open Patent Application Nos. 51-119727, 52-147638, 53-16048 and 56-151777.
Since the cathodic electrodeposition coating utilizes an electrochemical reaction in which cationic resin particles and other solid particles are insolubilized and deposited on a cathode-acting substrate article as the concentration of hydroxyl ions produced by the electrolysis of water increases at the vicinity of cathode, the solid content of the coating bath will decrease with time. Therefore, it is necessary to replenish various components to the bath from time to time. In case of electrodeposition enamels, it is simple and has been commercial practice to replenish pigments as pigment paste.
It is desirable for the pigment paste to have a pigment volume concentration (PVC) as high as possible. Such pigment paste has been conventionally prepared from a resin having the same secondary or tertiary amine function as he main film-forming resin. For example, polybutadiene-based cathodic electrodeposition coating systems disclosed in the above-cited references utilize a reaction product of partially epoxidized polybutadiene and a primary or secondary amine in the pigment paste. However, it has been found that when pigments are dispersed, particularly at a high PVC concentration, in an aqueous solution of a neutralizate of the above reaction product, difficulties can be encountered in achieving uniform dispersion of the pigment particles and also in the storage stability of the resulting pigment paste and coating compositions containing them.